ISO140 Marine Accessory: What It Does and How to Install It
By BOSS Audio Systems | Life at Full Volume | Published: 2026-10-31
Category: How-to Guides
The ISO140 is a 140-amp dual-battery smart isolator for boats. Learn what it does, what's in the kit, and follow a step-by-step installation with checkpoints.
Quick answer
The ISO140 is a 140-amp dual-battery smart isolator that keeps your starting battery charged while protecting it from being drained by accessory loads. Install it between the two batteries using the included cables, then verify the isolation and charging behavior before relying on it.
What the ISO140 actually does for a boat audio system
A dual-battery isolator separates your starting battery from your accessory or house battery. The alternator charges both when the engine runs, but the isolator prevents the house battery from pulling down the starting battery when the engine is off. That matters for marine audio because amplifiers and head units can draw significant current even when the engine is not running.
The ISO140 is rated at 140 amps, which is enough for many small-to-mid marine audio setups, but it is not a universal solution for every boat. If your alternator output or total accessory load exceeds that rating, you need a different approach. Also, the ISO140 is a smart isolator, so it decides when to connect or disconnect based on voltage, not a manual switch.
When the ISO140 is the right choice, and when it is not
The ISO140 fits boats with two batteries and a standard alternator charging system where you want automatic isolation without remembering to flip a switch. It is a good match for boats with a single starting battery and a single house battery running modest electronics.
It is not the right choice for systems with very high current demands, such as multiple large amplifiers running continuously, or for boats that already have a sophisticated battery management system. If your setup requires more than 140 amps of charging current or you need manual control for safety or racing rules, consider a different isolator or a manual switch.
Step-by-step ISO140 installation
- Disconnect both batteries: Turn off all power and disconnect the negative terminal on both the starting and house batteries before touching any wiring. Common mistake: skipping this step and risking a short circuit or shock. Always disconnect the negative terminals first.
- Plan the isolator location: Choose a dry, ventilated spot near the batteries but away from direct water spray and heat sources. The isolator has mounting holes; use the included screws to secure it. Common mistake: mounting it in a bilge or splash zone. Keep the isolator dry and accessible for inspection.
- Connect the starting battery positive cable: Use the included 14-inch 6 GA red cable to connect the starting battery positive terminal to the isolator's starting battery terminal. Crimp or solder the lug, then cover with the supplied red shrink tube. Common mistake: leaving the connection loose, which can cause arcing and heat. Tug-test each connection after crimping.
- Connect the house battery positive cable: Use the 26-inch 6 GA red cable (cut to length) to connect the house battery positive terminal to the isolator's house battery terminal. Cut only what you need and seal the end with shrink tube. Common mistake: cutting the cable too short before routing it through the boat. Route the cable first, then cut.
- Connect the ground cable: Use the 14-inch 4 GA black cable to connect the isolator's ground terminal to a clean, bare-metal ground point on the boat's common ground. Common mistake: grounding to a painted or corroded surface, which raises resistance. Sand the ground point to bare metal and use a star washer if possible.
- Reconnect the batteries and test: Reconnect the negative terminals. Measure voltage at both battery terminals with the engine off; they should be isolated. Start the engine and verify that both batteries rise to charging voltage. Common mistake: assuming it works without testing, which can leave you stranded. Test isolation and charging before your next trip.
ISO140 kit contents
- ISO140: 140 Amp Dual Battery Smart Isolator The 140-amp rating sets the maximum charging current the isolator can handle, so check your alternator output and accessory load before installing.
ISO140 - ISO140: Includes 14" (350 mm) 6 GA red cable and 14" (350 mm) 4 GA black cable with .3125” (8 mm) lug connectors These short cables are sized for typical battery-to-isolator connections, but you may need longer cables if your batteries are farther apart.
- ISO140: Includes a 26" (650 mm) 6 GA red cable (cut to length) with a .3125” (8 mm) lug connector The cut-to-length cable gives you some flexibility for routing, but plan your path before cutting to avoid waste.
- ISO140: Includes mounting screws, terminal nuts, and red shrink tube Having the right hardware on hand speeds up installation and helps you make secure, corrosion-resistant connections.
